The invention relates to a castor having a securing device for blocking the running and/or steering action of the running wheel mounted in a fork, which fork itself is mounted such that it can be pivoted about a vertical axis, having an actuating push rod, at the running-wheel end of which a braking-blocking and/or steering-blocking formation is formed, the push rod also interacting with fork-mounted steering-blocking mating protrusions.
A castor having a securing device of this type is known in a wide variety of embodiments; you are referred, for example, to DE-A 17 55 789 and DE-A 23 47 900. These forerunners provide, as the usable functional positions, for the fork and the running wheel to be blocked, also for the fork to be pivotable and the running wheel to be capable of running freelyxe2x80x94the trailing side being formed of its own accord herexe2x80x94and finally provides for a position in which the pivoting movement of the fork is blocked and the castor can rotate freely. This renders a castor, for all practical purposes, into a fixed castor. The actuating push rod, which can be moved into the different positions by a control cam which crosses over its axis, is subject to the action, in the restoring direction, of a helical compression spring which is plugged on to the stem of the push rod and is supported on a fork pin. Both the forerunners mentioned comprise a large number of parts and therefore involve high production and installation outlay.
It is an object of the invention to configure a castor of the generic type such that it is structurally more straightforward and more favourable for installation.
This object is achieved first and foremost, in the case of a castor with a securing device having the features of claim 1, by a combination part on which both the steering-blocking mating protrusions and the braking-blocking means, these being located in spaced-apart planes, are formed, the braking-blocking and/or steering-blocking formation of the push rod being located in a neutral position between these planes. Such a combination part reduces the number of parts. In addition, it performs tasks which go beyond the introduction of forces for the push rod. The above-mentioned elements are additionally stabilised in relation to one another. This also serves to simplify the installation. The initial switching state is a neutral position, from which the braking-blocking and/or steering-blocking formation can be displaced by an extremely short distance in opposite directions in order to move into the respective other functional position. It is advantageous then for the combination part to be formed as an integral part. This can be accomplished very well by moulding. Accordingly, it is not necessary for the combination parts to be combined from a plurality of individual parts to form a structural unit. Such a multifunctional combination part is accommodated, for protection, in a freely moveable, but rotationally blocked, manner in an inner space of the fork. The rotational blocking can easily be achieved by utilising the parallel arrangement, which is usually present anyway, of the fork legs as guide surfaces. The movement is oriented vertically. For all practical purposes, the combination part is just fitted in and also secured. In this respect, it is provided that the combination part is fastened on the push rod. The fastening is resilient. The spring functions as a connecting element between the combination part and the push rod. For long-term functioning, there is provided a wire fastening spring which, in the fastening state, is positioned in a circumferential groove of the push rod. The corresponding securing can be achieved, without the classic fastening means, by the push rods, at the running-wheel end, having an introduction cone for deflecting the wire spring in the course of latching installation. A structurally advantageous solution is provided if the wire fastening spring is a U-clip, the U-crosspiece of which has a deflection following approximately half the circumferential groove. This deflection is held securely in the region of the groove recess. It is advantageous in terms of arrangement here for the U-legs of the wire fastening spring to be accommodated in retaining grooves of the combination part. A further favourable feature of the invention is that the combination part has a braking section which is adapted to the running-wheel curvature and is formed underneath the plane of the braking-blocking means. This avoids exposed braking press-edges. The actual braking surface may also be provided with roughened formations, for example transverse ribbing located parallel in space to the geometrical axis of the running wheel. It is then provided that the wire spring passes through a chamber formed between the braking-blocking and/or steering-blocking formation and the braking section. This chamber is open in the direction away from the running wheel, so that the wire spring is accessible for release at all times. This facilitates installation, and also any possible dismantling operation. This is because, once the running wheel has been removed, the combination part can easily be drawn off, and replaced by a new combination part, in the axial direction of the push rod. For position adjustment of the securing device, it proves favourable to provide on the combination part an adjusting screw for supporting and adjusting the combination part in relation to a bearing or fork section of the castor, this section being disposed above the chamber. The adjustment is correspondingly stepless. The procedure here, in concrete terms, is such that the adjusting screw is accommodated by a thread in the combination part in the plane of the steering-blocking means. To this extent, the adjusting screw is also accommodated in a protected manner. The procedure here is also such that a through-passage opening is formed in the plane of the braking-blocking means in order to access the adjusting screw for actuation. Finally, the invention proposes that the steering-blocking mating protrusions are designed for rotational blocking, defining at least one position, of the fork. A rotary latching position going beyond the 360xc2x0 latching-position would then be located along the diametral line. Lastly, it proves advantageous for precision rotational blocking to be provided between the braking-blocking and/or steering-blocking formation and the braking-blocking means, which is closer to the running wheel. As a result, it is not just the case that the running wheel is braked, but also, at the same time, that the fork is prevented from rotating. Classic radially oriented tooth/gap engagement may be provided here.